Refrigeration system including a flexible sensor

ABSTRACT

A refrigeration system including a compressor configured to compress a refrigerant, a condenser in fluid communication with the compressor and configured to remove heat from the refrigerant, and an expansion valve in fluid communication with the condenser and configured to decrease a pressure of the refrigerant. The refrigeration system also includes an evaporator in fluid communication with the expansion valve and configured to facilitate heat exchange between the refrigerant and another fluid, and a sensor configured to bend to measure a property of the refrigeration system. The sensor including a flexible substrate and a conductive material applied to the flexible substrate and having a resistance that changes in response to bending of the flexible substrate to generate a signal indicative of the property.

BACKGROUND

The present invention relates to refrigeration systems and, particularly, to refrigeration systems that include sensors to measure properties of the refrigeration systems.

Refrigeration systems are commonly used in a variety of industrial and commercial applications to provide refrigeration to particular portions or processes of the applications. For example, commercial refrigeration systems are typically used to cool or freeze food product to permit longer storage of the food product. In some applications, it may be desirable to measure one or more properties of the refrigeration systems (e.g., air flow, refrigerant flow, fluid level, etc.) to monitor the status of the systems.

Presently, some air flow sensors exist that are relatively inexpensive, commercially available, and easily interfaced with control systems. For example, hot wire mass air flow (MAF) sensors, vane air flow (VAF) meters, and Karman vortex air flow meters are used to measure air flow properties. However, such sensors are commonly rendered non-functional in the presence of contaminants (e.g., dust, frost, liquid, etc.), making them less desirable for use in refrigeration systems. In addition, the unit cost of such sensors, while being acceptable for industrial and automotive markets, is typically cost prohibitive for commercial refrigeration systems. Furthermore, depending on the application, the life cycle of these sensors may be less than desirable.

SUMMARY

In one embodiment, the invention provides a refrigeration system including a compressor configured to compress a refrigerant, a condenser in fluid communication with the compressor and configured to remove heat from the refrigerant, and an expansion valve in fluid communication with the condenser and configured to decrease a pressure of the refrigerant. The refrigeration system also includes an evaporator in fluid communication with the expansion valve and configured to facilitate heat exchange between the refrigerant and another fluid, and a sensor configured to bend to measure a property of the refrigeration system. The sensor includes a flexible substrate and a conductive material applied to the flexible substrate. The conductive material has a resistance that changes in response to bending of the flexible substrate to generate a signal indicative of the property.

In another embodiment, the invention provides a method of measuring a property of a refrigeration system. The refrigeration system includes a compressor, a condenser in fluid communication with the compressor, an expansion valve in fluid communication with the condenser, and an evaporator in fluid communication with the expansion valve. The method includes providing a sensor including a flexible substrate and a conductive material applied to the flexible substrate. The conductive material has a resistance that changes in response to bending of the flexible substrate. The method also includes compressing a refrigerant with the compressor, removing heat from the refrigerant with the condenser, decreasing a pressure of the refrigerant with the expansion valve, exchanging heat between the refrigerant and another fluid with the evaporator, and bending the sensor to generate a signal indicative of a property of the refrigeration system.

In yet another embodiment, the invention provides an evaporative cooler including a housing having a least one vent and configured to contain water, a blower positioned within the housing and configured to draw air through the at least one vent, and an evaporator pad positioned adjacent to the at least one vent. The evaporative cooler also includes a pump configured to spray at least a portion of the evaporator pad with the water and a sensor configured to bend to measure a property of the evaporative cooler. The sensor includes a flexible substrate and a conductive material applied to the flexible substrate and having a resistance that changes in response to bending of the flexible substrate to generate a signal indicative of the property.

Other aspects of the invention will become apparent by consideration of the detailed description and accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic of a refrigeration system according to an embodiment of the invention.

FIG. 2A is planar view of a flexible sensor for use with the refrigeration system shown in FIG. 1.

FIG. 2B is a planar view of another flexible sensor for use with the refrigeration system shown in FIG. 1.

FIG. 3 is a schematic of a flexible sensor configured to measure a liquid flow.

FIG. 4 is a schematic of a flexible sensor configured to measure an air flow.

FIG. 5 is a schematic of a flexible sensor configured to measure a fluid level.

FIG. 6 is a schematic of a flexible sensor configured to measure a load on a secondary structure.

FIG. 7 is a schematic of another refrigeration system according to an embodiment of the present invention.

FIG. 8 is a cross-sectional view of an evaporative cooler according to an embodiment of the present invention.

DETAILED DESCRIPTION

Before any embodiments of the invention are explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the following drawings. The invention is capable of other embodiments and of being practiced or of being carried out in various ways. Also, it is to be understood that the phraseology and terminology used herein are for the purpose of description and should not be regarded as limiting. The use of “including,” “comprising,” or “having” and variations thereof herein is meant to encompass the items listed thereafter and equivalents thereof as well as additional items. Unless specified or limited otherwise, the terms “mounted,” “connected,” “supported,” and “coupled” and variations thereof are used broadly and encompass both direct and indirect mountings, connections, supports, and couplings. Further, “connected” and “coupled” are not restricted to physical or mechanical connections or couplings.

FIG. 1 illustrates a refrigeration system 10 including a compressor 14, a condenser 18, a receiver 22, an expansion valve 26, and an evaporator 30. In the illustrated embodiment, the refrigeration system 10 is used in a commercial setting (e.g., a grocery store) to maintain food product at a suitable refrigerated or freezing temperature. However, it should be readily apparent to one skilled in the art that the refrigeration system 10 may be adapted or configured for use in other applications (e.g., personal refrigerators, air-conditioning systems, oil refineries, chemical plants, metal refineries, etc.) where refrigeration is desired.

The illustrated compressor 14 is a single compressor operable to compress a vaporous refrigerant. However, the compressor 14 may be replaced by multiple compressors arranged in parallel or in series to compress the refrigerant. The compressor(s) 14 may be, for example, a centrifugal compressor, a rotary screw compressor, a reciprocating compressor, or the like. In the illustrated embodiment, the compressor 14 compresses a refrigerant and delivers the compressed refrigerant to the condenser 18.

The condenser 18 is positioned downstream of the compressor 14 to receive the vaporous, compressed refrigerant. In the illustrated embodiment, the condenser 18 is an air-cooled condenser that includes a condenser coil 34 and a fan 38. The fan 38 directs and propels air over the condenser coil 34 to remove heat from the refrigerant within the condenser coil 34. In other embodiments, the condenser 18 may be a water-cooled condenser. As the condenser 18 removes heat from the vaporous refrigerant, the refrigerant changes into a liquid refrigerant and is delivered to the receiver 22.

The receiver 22 is positioned downstream of the condenser 18 to receive the liquid refrigerant from the condenser 18. The receiver 22 is configured to store or retain a supply of liquid refrigerant. As shown in FIG. 1, a portion of the refrigerant within the receiver may also be vaporous. The refrigerant enters the receiver 22 through a top of the receiver 22 and exits the receiver through a bottom to ensure only liquid refrigerant leaves the receiver 22.

The expansion valve 26 is positioned downstream of the receiver 22 to receive the liquid refrigerant from the receiver 22. The expansion valve 26 may be any suitable type of throttle valve that abruptly decreases the pressure of the liquid refrigerant. As the liquid refrigerant decreases in pressure, a portion of the refrigerant vaporizes and, thereby, further decreases in temperature. The cool refrigerant exiting the expansion valve 26 is directed toward the evaporator 30.

The evaporator 30 is positioned downstream of the expansion valve 26 to receive the cool refrigerant. The evaporator 30 includes an evaporator coil 42 and a fan 46 configured to facilitate heat exchange between the refrigerant and a secondary fluid (e.g., air) by directing and propelling the secondary fluid over the evaporator coil 42. The refrigerant warms and evaporates in the evaporator 30 and is circulated back toward the compressor 14.

The illustrated refrigeration system 10 also includes a refrigerated display case 50, or merchandiser, operable to store and display food product at a reduced temperature. In the illustrated embodiment, the display case 50 includes a housing 54 defining a product display area 58, a door 62 coupled to the housing 54, and shelves 66 positioned within the product display area 58 to support the food product. The illustrated evaporator 30 is located within an air passageway 70 of the housing 54 such that the cool refrigerant in the evaporator coil 42 exchanges heat with air flowing through the display case 50, thereby maintaining the reduced temperature within the product display area 58.

In operation, the compressor 14 compresses a gaseous refrigeration and directs the compressed refrigerant to the condenser 18 where the refrigerant is cooled and condensed into a liquid refrigerant. In some embodiments, such as the illustrated embodiment, the liquid refrigerant may be temporarily stored in the receiver 22 prior to being directed toward the evaporator 30. The liquid refrigerant is pulled from the receiver 22 and forced through the expansion valve 26 to convert the refrigerant into a two-phase fluid. The two-phase refrigerant absorbs heat from air being directed through the evaporator 30 by the fan 46. The refrigerant generally leaves the evaporator 30 in a superheated condition and is routed back to the compressor 14 for recycling. The cooled air exiting the evaporator 30 is directed through the air passageway and is introduced into the product display area 58, where it will remove heat from the displayed food product and maintain the food product at the desired temperature.

As shown in FIG. 1, the illustrated refrigeration system 10 also includes a plurality of flexible sensors 74A-74P. The sensors 74A-74P are shown schematically to illustrate their general position relative to the other components of the refrigeration system 10. Each flexible sensor 74A-74P measures one or more system properties and outputs the measured property to sensing and conditioning electronics 78 (FIGS. 3, 4, 5, and 6) to notify an operator of the current status of the refrigeration system 10. In some embodiments, the refrigeration system 10 may include only one or a few of the illustrated sensors 74A-74P, depending on which system properties the operator wishes to monitor. In other embodiments, the refrigeration system 10 may include sensors located at additional or alternative locations to measure other system properties.

FIGS. 2A and 2B illustrate two constructions of flexible sensors 82A, 82B for use with the refrigeration system 10 shown in FIG. 1. In the illustrated embodiment, both sensors 82A, 82B include generally the same components and function in a generally similar manner, and, thereby, like parts are given the same reference numerals. In some embodiments, such as the illustrated embodiment, each flexible sensor is a Bend Sensor® provided by Flexpoint Sensor Systems, Inc. of Draper, Utah.

Each sensor 82A, 82B includes a flexible substrate 86, a conductive material 90 coupled to the substrate 86, a sleeve 94 positioned around the substrate 86, and a connection area 98. The substrate 86 is configured to deflect, or bend, when a force is applied to the sensor 82A, 82B. In the illustrated embodiment, the substrate 86 repeatably and reliably bends by various degrees proportional to the applied force. Once the force is removed or stopped, the substrate 86 moves back to a substantially straight position, as shown in FIGS. 2A and 2B.

The conductive material 90 is coupled or applied to the substrate 86 to deflect with the substrate 86. As the conductive material 90 bends, the resistance of the material 90 changes. Therefore, the sensor 82A, 82B will output a different voltage or current based on the degree of deflection of the material 90. In the illustrated embodiment, the conductive material 90 is only shown coupled to one side of the substrate 86. However, it should be readily apparent that the material 90 may be coupled in a similar manner to the opposite side of the substrate 86 such that the sensor 82A, 82B not only measures the degree of deflection, but also the direction of deflection. For example, when the flexible sensor 82A, 82B deflects in one direction, the sensor 82A, 82B outputs a positive voltage. When the flexible sensor 82A, 82B deflects in the opposite direction, the sensor 82A, 82B outputs a negative voltage. In some embodiments, the material 90 may be a conductive ink printed on the substrate 86.

The sleeve 94, or sheath, surrounds the substrate 86 and the conductive material 90 to protect the flexible sensor 82A, 82B. In the illustrated embodiment, the sleeve 94 seals the substrate 86 from the environment to inhibit contaminants (e.g., dust, frost, liquid, etc.) from contacting conductive material 90. In some embodiments, the sleeve 94 has bend characteristics that are substantially similar to the flexible substrate 86.

The connection area 98 facilitates electrically coupling the sensors 82A, 82B to the sensing and conditioning electronics 78. Referring to the construction shown in FIG. 2A, the connection area 98 includes a plug 102 to allow quick connecting and disconnecting with the electronics 78. Referring to the construction shown in FIG. 2B, the connection area 98 includes electrical leads 106 to allow the sensor 82A, 82B to be spaced further away from the electronics 78.

FIG. 3 illustrates the first flexible sensor 82A in a fluid conduit 110 to measure a liquid flow. In the illustrated embodiment, the flexible sensor 82A is positioned between first and second large body resistors 114, 118 and electrically coupled to the sensing and conditioning electronics 78. A low voltage, low current DC voltage is applied to the resistors 114, 118 to warm the resistors 114, 118 and, thereby, heat the sensor 82A. Such heating keeps the sensor 82A from adhering, or freezing, to the resistors 114, 118 or the conduit 110. As a liquid (e.g., refrigerant, oil, etc.) flows over and past the flexible sensor 82A, the sensor 82A deflects and outputs a signal to the electronics 78 indicative of the direction of flow, the speed of the flow, and/or the rate of change of the flow over time. Additionally, the signal may be used to calculate the volume of liquid flow.

For example, in one construction, the flexible sensor 82A may be used to monitor refrigerant flow in the refrigeration system 10. In such a construction, the sensor 82A may be positioned within any conduit, or line, of the refrigeration system 10 shown in FIG. 1 to monitor the speed and/or volume of refrigerant flowing through the conduit.

In another construction, the sensor 82A may be positioned downstream of the expansion valve 26 to monitor the status of the valve 26. In such a construction, the sensor 82A is positioned generally at the location of the sensor 74A in FIG. 1. Based on the measured speed or volume of the refrigerant, the sensor 82A can determine if the valve 26 fails to open, fails to close, or improperly throttles the refrigerant exiting the valve 26. The electronics 78 may then trigger an alarm or warning to notify an operator of this valve failure. For example, in some embodiments, the alarm may be a displayed warning message, an audible noise, a flashing light, an email notification, a voice message, a pager alert, or the like. In addition, the flexible sensor 82A can use the measured refrigerant flow to determine a position of the expansion valve 26 (e.g., opened, closed, or an intermediate position) and output the position information to the operator with the electronics 78.

In yet another construction, the sensor 82A may be positioned downstream of the compressor 14 to monitor the status of the compressor 14. In such a construction, the sensor 82A is positioned generally at the location of the sensor 74B in FIG. 1. Based on the measured refrigerant flow output by the compressor 14, the sensor 82A and the electronics 78 can determine a run time of the compressor 14 and output the run time to an operator.

In a further construction, the sensor 82A may be positioned within the compressor 14 to monitor an oil flow inside the compressor 14. In such a construction, the sensor 82A is positioned generally at the location of the sensor 74C in FIG. 1. Based on the oil flow measured by the sensor 82A, the electronics 78 can notify an operator if the compressor 14 is running low on oil or if too much oil has been added to the compressor 14.

FIG. 4 illustrates the first flexible sensor 82A in an air passageway 122 to measure an air flow. Similar to the construction described above with reference to FIG. 3, the sensor 82A is positioned between the two large body resistors 114, 118 and electrically coupled to the sensing and conditioning electronics 78. As air flows over and past the flexible sensor 82A, the sensor 82A deflects and outputs a signal to the electronics 78 indicative of the direction of flow, the speed of the flow, and/or the rate of change of the flow over time. Additionally, the signal may be used to calculate the volume of air flow.

In one construction, the flexible sensor 82A is used to measure an off coil air velocity at the evaporator 30. In such a construction, the sensor 82A is positioned generally at the location of the sensor 74D in FIG. 1. When the evaporator 30 is operating properly, air flows past the evaporator coil 42 and deflects the sensor 82A. However, over time water vapor in the air may condense and freeze on the surface of the evaporator coil 42 in certain ambient conditions, creating a frost build-up. Significant frost build-up reduces the evaporator coil performance by reducing the air flow through the coil 42. When the air flow through the coil 42 is reduced, the sensor 82A is no longer deflected (or not deflected as much), changing the signal output to the electronics 78. The electronics 78 can then trigger or initiate a demand defrost to remove the frost from the evaporator coil. In some embodiments, the electronics 78 can trigger an alarm or warning to notify an operator to initiate the demand defrost. In other embodiments, the electronics 78 may initiate the demand defrost automatically.

In another construction, the flexible sensor 82A is used to determine a fan failure. In such a construction, the sensor 82A is positioned generally at the location of sensor 74E or sensor 74F in FIG. 1 to monitor the condenser fan 38 or the evaporator fan 46, respectively. When the fans 38, 46 are functioning properly (e.g., propelling air over their respective coils 34, 42), the sensors 82A are deflected by the air flow. However, if either fan 38, 46 stops running, the corresponding sensor 82A will no longer be deflected, changing the signal output to the electronics 78. The electronics 78 may then trigger an alarm or warning to notify an operator of this failure.

In yet another construction, the flexible sensor 82A is used to determine if an air return grille 126 of the display case 50 is blocked. In such a construction, the sensor 82A is positioned generally at the location of the sensor 74G in FIG. 1. During normal operation, air flows from the evaporator 30, through the air passageway 70, through the product display area 58, and back to the air passageway 70 through the air return grille 126. As the air flows through the grille 126, the sensor 82A is deflected and outputs a corresponding signal to the electronics 78. If the grille 126 becomes blocked by foreign material, air will no longer flow through the grille 126 and deflect the sensor 82A, changing the signal output to the electronics 78. The electronics 78 may then trigger an alarm or warning to notify an operator of the blockage.

In a similar construction, the flexible sensor 82A is used to determine if the condenser 18 is blocked. In such a construction, the sensor 82A is positioned generally at the location of the sensor 74H in FIG. 1. The sensor 82A is slightly upstream of the condenser fan 38 to monitor when the condenser fan 38 pulls ambient air through the condenser 18. As air is pulled through the condenser 18 by the fan 38, the sensor 82A is deflected and outputs a corresponding signal to the electronics 78. If the condenser 18 becomes blocked (e.g., a grille covering the fan 38 becomes blocked), the fan 38 will no longer pull air and the sensor 82A will no longer be deflected, changing the signal output to the electronics 78. The electronics 78 may then trigger an alarm or warning to notify an operator of the blockage.

FIG. 5 illustrates the first flexible sensor 82A configured to measure a fluid level. In the illustrated embodiment, the flexible sensor 82A is positioned adjacent to only one large body resistor 114; however, in other embodiments, the sensor 82A may be positioned between two resistors. Similar to the construction described above with reference to FIG. 3, the flexible sensor 82A is electrically coupled to the sensing and conditioning electronics 78.

As shown in FIG. 5, a float 130 is coupled to an end of the sensor 82A opposite from a support 134, or wall. When the fluid level rises and contacts the float 130, the float 130 rises and deflects the sensor 82A. In some configurations, the sensor 82A may start at the substantially straight position (shown as a solid line) and move to a bent position (shown in phantom lines) to measure an increase in the fluid level. In other configurations, the sensor 82A may start at a bent position and move to the substantially straight position to measure a decrease in the fluid level. As such, the flexible sensor 82A may be used to measure when the fluid level is greater than or less than a desired, or acceptable, level.

In one construction, the flexible sensor 82A is used to measure a refrigerant level (e.g., a refrigerant charge) within the receiver 22. In such a construction, the sensor 82A is positioned generally at the location of the sensor 741 in FIG. 1. The sensor 82A is coupled to a wall of the receiver 22 and extends inwardly in the substantially straight position, corresponding to an acceptable refrigerant level. If the refrigerant level rises, the sensor 82A is deflected upwardly due to the float 130 rising with the refrigerant, changing the signal output by the sensor 82A (e.g., to a positive voltage) to the electronics 78. If the refrigerant level falls, the sensor 82A deflects downwardly due to gravity, changing the signal output by the sensor 82A (e.g., to a negative voltage) to the electronics 78. The electronics 78 may then trigger an alarm or warning to notify an operator of the changed refrigerant level. Although the flexible sensor 82A is described starting at the substantially straight position, it should be readily apparent to one skilled in the art that the sensor 82A may start at a bent position, either upwardly or downwardly, that corresponds to the acceptable refrigerant level.

In another construction, the flexible sensor 82A is used to determine if a drain 138 of the display case 50 is clogged or blocked. In such a construction, the sensor 82A is positioned generally at the location of the sensor 74J in FIG. 1. The drain 138 is positioned in a lower portion 142 of the housing 54 such that liquid that accumulates in the product display area 58 (e.g., melted frost, spilled liquid food product, etc.) is automatically drained from the display case 50. In the illustrated embodiment, the sensor 82A is positioned directly adjacent to the lower portion 142 of the housing 54. If the drain 138 becomes blocked or clogged, liquid will no longer drain from the display case 50 and will begin to accumulate on the lower portion 142 of the housing 54. As the liquid accumulates, the sensor 82A deflects upwardly, changing the signal output to the electronics 78. The electronics 78 may then trigger an alarm or warning to notify an operator to check the drain 138.

In a further construction, the sensor 82A measures an oil level within the compressor 14. In such a construction, the sensor 82A is positioned generally at the location of the sensor 74C in FIG. 1. Due to turbulence within the compressor 14 (e.g., oil turbulence), it may be less desirable to use a float arrangement to measure the oil level in the compressor 14. As such, the sensor 82A is coupled to a gear driven piece of the compressor 14, such as a shaft, that rotates based on the oil level within the compressor 14. As the oil level rises, the shaft rotates in a first direction so that the sensor 82A wraps around the shaft. The resistance of the sensor 82A, and thereby the signal output to the sensing and conditioning electronics 78, increases as the sensor 82A wraps around the shaft. As the oil level falls, the shaft rotates in a reverse direction so that the sensor 82A unwraps from the shaft. The resistance of the sensor 82A, and thereby the signal output to the electronics 78, decreases as the sensor 82A unwraps from the shaft. Based on the signal output by the sensor 82A, the electronics 78 may notify an operator of the current oil level or trigger an alarm or warning if the oil level rises above or falls below an acceptable level.

FIG. 6 illustrates the second flexible sensor 82B configured to measure an applied force or to monitor movement of a secondary structure 146. In the illustrated embodiment, the flexible sensor 82B is disposed within an elastic material 150 and coupled to the secondary structure 146 (e.g., a hinge, a shelf, a switch, or the like) such that any movement of the secondary structure 146 is transferred to the sensor 82B. As one portion of the secondary structure 146 moves relative to another portion of the secondary structure 146 due to the applied force, bending, rotation, or the like, the sensor 82B deflects a proportionate amount. Similar to the construction discussed above with reference to FIG. 3, the sensor 82B is electrically coupled to the sensing and conditioning electronics 78.

In one construction, the secondary structure 146 is a hinge that couples the door 62 to the housing 54 of the display case 50. For example, the flexible sensor 82B is coupled to the hinge such that one end of the sensor 82Bis securely fastened to a first half of the hinge, and another end of the sensor 82B is securely fastened to a second half of the hinge. In such a construction, the sensor 82B is positioned generally at the location of the sensor 74K in FIG. 1. When the door 62 is closed, the hinge is substantially straight such that the sensor 82B is likewise substantially straight. As the door 62 opens, the first half of the hinge rotates relative to the second half, deflecting the sensor 82B and changing the signal output to the electronics 78. If the door 62 is left open for a prolonged period of time or if the door 62 is left slightly ajar, such that the deflection of the sensor 82B is small, the electronics 78 can trigger an alarm or warning to notify an operator to check the door 62.

In another construction, the secondary structure 146 is one of the shelves 66 within the product display area 58 of the display case 50. In such a construction, the sensor 82B is positioned generally at the location of the sensors 74L in FIG. 1. The flexible sensor 82B is used to monitor a load condition (e.g., a weight of food product) on the shelf 66, rather than having to constantly visually monitor the shelf 66. When the shelf 66 is filled with food product, the shelf 66 deflects, causing the sensor 82B to deflect and output a corresponding signal to the electronics 78. As the food product is removed from the shelf 66, the shelf 66 deflects less and less until the shelf 66, and thereby the sensor 82B, substantially straightens. When the shelf 66 and the sensor 82B are only deflected a small amount, the sensor 82B outputs a different signal to the electronics 78. The electronics 78 can then trigger an alarm or warning to notify an operator to check and restock the shelf 66, if necessary.

In yet another construction, the secondary structure 146 is a switch of a circuit breaker 154 for the product display case 50. In such a construction, the sensor 82B is positioned generally at the location of the sensor 74M in FIG. 1. The illustrated circuit breaker 154 is electrically coupled to the evaporator 30 to provide power to the evaporator fan 46. However, it should be readily apparent that the circuit breaker 154 may be electrically coupled to other components of the refrigeration system 10 and/or the display case 50 (e.g., lights, fans, etc.). The flexible sensor 82B is coupled to one of the switches of the circuit breaker 154 such that an operator is given instant notification if one of the circuits becomes tripped. For example, when the circuit is closed, the switch is flipped to one side, bending the sensor 82B to output a positive voltage. When the circuit is opened, the switch is flipped to the other side, bending the sensor 82B to output a negative voltage. The change in voltages from positive to negative (or vise versa) is output to the electronics 78, which triggers an alarm or warning to notify the operator of the tripped circuit.

In still another construction, the secondary structure 146 is a contactor. As shown in FIG. 1, a first contactor 158 is electrically coupled to the compressor 14 to provide power to the compressor 14 and a second contactor 162 is electrically coupled to the condenser 18 to provide power to the condenser fan 38. In such a construction, the sensor 82B is positioned generally at the location of the sensor 74N and/or the sensor 74P in FIG. 1. As such, the sensor 82B is coupled to a switch of each contactor 158, 162 to monitor the position of the switch in a similar manner to the circuit breaker 154 described above. The sensor 82B provides information to an operator regarding a status of the contactors 158, 162. For example, the sensor 82B can monitor when the switches move to a position where the contactors 158, 162 are providing power to the compressor 14 and condenser 18, respectively, so the operator knows if the compressor 14 and the condenser 18 should be running.

FIG. 7 illustrates another refrigeration system 200 according to an embodiment of the invention. The refrigeration system 200 includes a first refrigeration unit 210 and a second refrigeration unit 212. Similar to the refrigeration system 10 discussed above with reference to FIG. 1, the first refrigeration unit 210, or primary refrigeration loop, includes compressors 214, a condenser 218, a receiver 222, an expansion valve 226, and an evaporator 230. In the illustrated embodiment, three compressors 214 are arranged in parallel; however, it should be readily apparent that fewer or more compressors may be included, or the compressors 214 may be arranged in series. The first refrigeration unit 210 circulates a first, or primary, refrigerant that is in a heat exchange relationship with a second refrigerant of the second refrigeration unit 212 at the evaporator 230. Reference is hereby made to the description of the refrigeration system 10 above for discussion of the operation of the first refrigeration unit 210.

The illustrated second refrigeration unit 212, or secondary refrigeration loop, includes the evaporator 230, a pump 234, and three display cases 250. The pump 234 may be any positive displacement pump, centrifugal pump, or the like suitable to move and circulate the second refrigerant. The illustrated pump 234 generates a driving force to draw the second refrigerant from the evaporator 230 and direct the second refrigerant toward and through the display cases 250.

The display cases 250 may be similar to the display case 50 discussed above with reference to FIG. 1. In the illustrated embodiment, the second refrigeration unit 212 includes three display cases 250 arranged in parallel. However, in other embodiments, the second refrigeration unit 212 may include fewer or more display cases 250 depending on the capacity of the refrigeration system 200. Each display case 250 includes an evaporator or heat exchanger configured to receive the second refrigerant in a liquid or liquid/vapor state and facilitate heat exchange between the second refrigerant and air within the display case 250. The display cases 250 thereby maintain a temperature suitable for refrigerating or freezing food product within the cases 250.

In operation, the second refrigerant is circulated through the second refrigeration unit 212 by the pump 234. In other embodiments, a compressor upstream of the evaporator 230 compresses and circulates the second refrigerant. At the evaporator 230, the second refrigerant comes into a heat exchange relationship with the first refrigerant in the first refrigeration unit 210 to remove heat from the second refrigerant. The second refrigerant is then drawn through the pump 234 and directed toward the display cases 250. The second refrigerant exchanges heat with the air in the display cases 250 to remove heat from the air. Then, the second refrigerant is directed back toward the evaporator 230 to once again remove heat from the second refrigerant with the first refrigerant.

In the illustrated embodiment, the refrigeration system 200 also includes a flexible sensor 274 positioned in the second refrigeration unit 212. Although only one sensor 274 is shown, it should be readily apparent to one skilled in the art that the refrigeration system 200 may include multiple flexible sensors positioned throughout the second refrigeration unit 212, as well as throughout the first refrigeration unit 210, or at any location corresponding to the sensors 74A-74P discussed above with reference to FIG. 1. The flexible sensor 274 is similar to the flexible sensor 82A discussed above with reference to FIG. 2A, and measures a property of the second refrigeration unit 212. The illustrated sensor 274 is positioned to measure a fluid flow (e.g., a refrigerant flow) downstream of the pump 234. By measuring the speed and/or volume of the fluid flow, the sensor 274 can determine if the pump 234 is functioning properly. If necessary, the sensor 274 can trigger an alarm or warning to notify an operator that the pump 234 (or other portion of the second refrigeration unit 212) needs maintenance.

FIG. 8 illustrates an evaporative cooler 300 according to an embodiment of the invention. The evaporative cooler 300, or swamp cooler, can be used as a stand-alone cooling system or in combination with either of the refrigeration systems 10, 200 discussed above to provide additional or supplemental cooling. The illustrated evaporative cooler 300 includes a housing 304, a blower 308 positioned within the housing 304, evaporator pads 312, and a pump 316. The housing 304 is configured to surround, protect, and support the other components of the evaporative cooler 300. In the illustrated embodiment, the housing 304 includes vents 320 to facilitate air flow into the evaporative cooler 300 and is configured to retain a supply of water 324. The housing 304 also includes a duct 328 configured to direct a cool air flow out of the evaporative cooler 300 and toward the desired location. In some embodiments, the duct 328 may direct the cool air flow into a secondary heat exchanger (e.g., an evaporator) such that the cool air flow does not come into direct contact with the environment being cooled.

The illustrated blower 308 includes a fan 332 (e.g., a centrifugal fan) and a motor 336 coupled to the fan 332 to drive the fan 332. In the illustrated embodiment, both the fan 332 and the motor 336 are supported within the housing 304. In other embodiments, the motor 336 may be positioned outside of the housing 204 to allow easier access to the motor 226. The fan 223 draws the air flow into the evaporative cooler 300 through the vents 320 and directs the cool air flow out through the duct 328.

The evaporator pads 312 are positioned within the housing 304 adjacent to the vents 320. The evaporator pads 312 may be composed of, for example, excelsior, melamin paper, or plastic. The evaporator pads 312 are configured to temporarily retain water to cool the air flow. As the air flow passes through the pads 312, heat in the air flow evaporates the water in the pads 312, cooling the air flow. The cool air flow then flows through the duct 328 to the desired location. As shown in FIG. 8, the cool air flow may pass over the water supply 324 in the housing 304 to further cool and humidify the air flow prior to entering the duct 328.

The pump 316 is positioned within the housing 304 and is in communication with the water supply 324. The pump 316 supplies water to the evaporator pads 312 to remoisten the pads 312 when the air flow evaporators the water on the pads 312. A water distribution line 340 is coupled to the pump 316 to direct water from the pump 316 onto the pads 312. The illustrated distribution line 340 includes two outlets 344 configured to evenly spray the water over the evaporator pads 312. When the evaporative cooler 300 is running, the pump 316 draws water from the water supply 324 and directs the water through the distribution line 340. The water is ejected from the distribution line 340 at the outlets 344 and sprayed onto the evaporator pads 312 to reapply water to the pads 312 such that the air flow through the pads 312 is continuously cooled.

In the illustrated embodiment, the evaporative cooler 300 also includes three flexible sensors 374A, 374B, 374C. The flexible sensors 374A, 374B, 374C are similar to the sensor 82A discussed above with reference to FIG. 2A and are used to measure properties of the evaporative cooler 300. For example, the first sensor 374A is positioned adjacent to the water supply 324 to measure the water level within the housing 304. As such, the first sensor 374A may be configured similar to the construction shown in FIG. 5. That is, the first sensor 374A may include a float and bend upwardly to notify an operator that the water level is becoming too high, or bend downwardly to notify the operator that the water level is becoming too low. Similar to the previous constructions, the sensor 374A is coupled to sensing and conditioning electronics that trigger an alarm or warning to notify the operator of either change in the water level.

The second sensor 374B and the third sensor 374C are positioned adjacent to the outlets 344 of the water distribution lines 340. When the evaporative cooler 300 is not in operation and water is not being sprayed from the distribution line 340, the sensors 374B, 374C are substantially straight. As water is sprayed out of the distribution line 340 and onto the evaporator pads 312, the sensors 374B, 374C are deflected by the sprayed water. Deflecting the sensors 374B, 374C changes the resistance of the conductive material 90 and, thereby, the signal output by the sensors 374B, 374C to the sensing and conditioning electronics. The electronics then notify an operator that the evaporative cooler 300 is in operation and functioning properly. If one the sensors 374B, 374C is not deflected during operation of the evaporative cooler 300, the electronics can notify the operator to check the corresponding distribution line 340 for a clog or rupture.

Flexible sensors provide a reliable means to measure various properties of refrigeration systems. In particular, the sensors are impervious to the operating environment of a commercial refrigeration system. For example, the sensors are not affected by dust, moisture, low operating temperatures of refrigerant, or varying temperatures of an air flow. In addition, the sensor can withstand in excess of thirty million cycles, but are still relatively cost effective. Furthermore, the flexible sensors include no moving parts or active electronic devices that may need servicing or replacement over time.

Various features and advantages of the invention are set forth in the following claims. 

1. A refrigeration system comprising: a compressor configured to compress a refrigerant; a condenser in fluid communication with the compressor and configured to remove heat from the refrigerant; an expansion valve in fluid communication with the condenser and configured to decrease a pressure of the refrigerant; an evaporator in fluid communication with the expansion valve and configured to facilitate heat exchange between the refrigerant and another fluid; and a sensor configured to bend to measure a property of the refrigeration system, the sensor including a flexible substrate, and a conductive material applied to the flexible substrate and having a resistance that changes in response to bending of the flexible substrate to generate a signal indicative of the property.
 2. The refrigeration system of claim 1, wherein the sensor includes a sleeve positioned around at least a portion of the flexible substrate.
 3. The refrigeration system of claim 1, wherein the property is a liquid flow within at least one component of the refrigeration system.
 4. The refrigeration system of claim 3, wherein the liquid flow is a refrigerant flow.
 5. The refrigeration system of claim 3, wherein the liquid flow is an oil flow.
 6. The refrigeration system of claim 3, wherein failure of the expansion valve is determined by measuring the liquid flow with the sensor.
 7. The refrigeration system of claim 3, wherein a position of the expansion valve is determined by measuring the liquid flow with the sensor.
 8. The refrigeration system of claim 3, wherein a run time of the compressor is determined by measuring the liquid flow with the sensor.
 9. The refrigeration system of claim 1, wherein the property is an air flow.
 10. The refrigeration system of claim 9, wherein a demand defrost is triggered by measuring the air flow with the sensor.
 11. The refrigeration system of claim 9, wherein at least one of the condenser and the evaporator includes a fan, and wherein failure of the fan is determined by measuring the air flow with the sensor.
 12. The refrigeration system of claim 9, further comprising a display case including an air return grille, wherein blockage of the air return grille is determined by measuring the air flow with the sensor.
 13. The refrigeration system of claim 9, wherein blockage of the condenser is determined by measuring the air flow with the sensor.
 14. The refrigeration system of claim 1, wherein the property is a fluid level within at least one component of the refrigeration system.
 15. The refrigeration system of claim 14, further comprising a receiver configured to hold a portion of the refrigerant, wherein the fluid level is a refrigerant level within the receiver.
 16. The refrigeration system of claim 14, wherein the fluid level is an oil level within the compressor.
 17. The refrigeration system of claim 14, further comprising a display case including a drain, wherein blockage of the drain is determined by measuring the fluid level within the display case with the sensor.
 18. The refrigeration system of claim 1, further comprising a display case including a door, wherein the property is a position of the door.
 19. The refrigeration system of claim 1, further comprising a display case including a shelf, wherein the property is a load condition of the shelf.
 20. The refrigeration system of claim 1, further comprising a circuit breaker, wherein the property is a status of the circuit breaker.
 21. The refrigeration system of claim 1, further comprising a contactor configured to transmit power to at least one component of the refrigeration system, wherein the property is a status of the contactor.
 22. The refrigeration system of claim 1, further comprising a second refrigeration unit configured to circulate a second refrigerant that exchanges heat with the first-mentioned refrigerant, wherein the property is a fluid flow within the second refrigeration unit.
 23. A method of measuring a property of a refrigeration system, the refrigeration system including a compressor, a condenser in fluid communication with the compressor, an expansion valve in fluid communication with the condenser, and an evaporator in fluid communication with the expansion valve, the method comprising: providing a sensor including a flexible substrate and a conductive material applied to the flexible substrate, the conductive material having a resistance that changes in response to bending of the flexible substrate; compressing a refrigerant with the compressor; removing heat from the refrigerant with the condenser; decreasing a pressure of the refrigerant with the expansion valve; exchanging heat between the refrigerant and another fluid with the evaporator; and bending the sensor to generate a signal indicative of a property of the refrigeration system.
 24. The method of claim 23, wherein bending the sensor includes bending the sensor to measure a liquid flow within at least one component of the refrigeration system.
 25. The method of claim 24, wherein the liquid flow is a refrigerant flow.
 26. The method of claim 24, wherein the liquid flow is an oil flow.
 27. The method of claim 24, wherein bending the sensor to measure a liquid flow includes bending the sensor to determine a failure of the expansion valve.
 28. The method of claim 24, wherein bending the sensor to measure a liquid flow includes bending the sensor to determine a position of the expansion valve.
 29. The method of claim 24, wherein bending the sensor to measure a liquid flow includes bending the sensor to determine a run time of the compressor.
 30. The method of claim 23, wherein bending the sensor includes bending the sensor to measure an air flow within at least one component of the refrigeration system.
 31. The method of claim 30, wherein bending the sensor to measure an air flow includes bending the sensor to trigger a demand defrost.
 32. The method of claim 30, wherein at least one of the condenser and the evaporator includes a fan, and wherein bending the sensor to measure an air flow includes bending the sensor to determine a fan failure.
 33. The method of claim 30, wherein the refrigeration system further includes a display case having an air return grille, and wherein bending the sensor to measure an air flow includes bending the sensor to determine blockage of the air return grille.
 34. The method of claim 30, wherein bending the sensor to measure an air flow includes bending the sensor to determine blockage of the condenser.
 35. The method of claim 23, wherein bending the sensor includes bending the sensor to measure a fluid level within at least one component of the refrigeration system.
 36. The method of claim 35, wherein the refrigerant system further includes a receiver configured to hold a portion of the refrigerant, and wherein bending the sensor to measure a fluid level includes bending the sensor to measure a refrigerant level within the receiver.
 37. The method of claim 35, wherein bending the sensor to measure a fluid level includes bending the sensor to measure an oil level within the compressor.
 38. The method of claim 35, wherein the refrigeration system further includes a display case having a drain, and wherein bending the sensor to measure a fluid level includes bending the sensor to determine blockage of the drain.
 39. The method of claim 23, wherein the refrigeration system further includes a display case having a door, and wherein bending the sensor includes bending the sensor to determine a position of the door.
 40. The method of claim 23, wherein the refrigeration system further includes a display case having a shelf, and wherein bending the sensor includes bending the sensor to determine a load condition of the shelf.
 41. The method of claim 23, wherein the refrigeration system further includes a circuit breaker, and wherein bending the sensor includes bending the sensor to determine a status of the circuit breaker.
 42. The method of claim 23, wherein the refrigeration system further includes a contactor configured to transmit power to at least one component of the refrigeration system, and wherein bending the sensor includes bending the sensor to determine a status of the contactor.
 43. The method of claim 23, wherein the refrigeration system further includes a second refrigeration unit configured to circulate a second refrigerant that exchanges heat with the first-mentioned refrigerant, and wherein bending the sensor includes bending the sensor to measure a fluid flow within the second refrigeration unit.
 44. An evaporative cooler comprising: a housing having at least one vent and configured to contain water; a blower positioned within the housing and configured to draw air through the at least one vent; an evaporator pad positioned adjacent to the at least one vent; a pump configured to spray at least a portion of the evaporator pad with the water; and a sensor configured to bend to measure a property of the evaporative cooler, the sensor including a flexible substrate, and a conductive material applied to the flexible substrate and having a resistance that changes in response to bending of the flexible substrate to generate a signal indicative of the property.
 45. The evaporative cooler of claim 44, wherein the property is a water level within the housing.
 46. The evaporative cooler of claim 44, wherein the property is a spray flow from the pump. 